Question about 1992 Ford F250
2nd master cylinder because I thought the first was bad. Bled the brakes 3 times, but still have a pedal that starts out strong then goes slowly to floor. Can't find any leaks either. Please help. Reg.
I would strongly recommend checking your trucks R.A.B.S. (Rear Antilock Brake System) valve . It is located on the left frame rail just under where your left foot would rest . They can leak internally and exhibit the problems you are describing (loss of pedal , with no fluid loss) .
It is highly unlikely that a power booster would cause this , as a failed booster will show itself in these ways . 1) a hissing sound when you apply the brakes (indicates a vacumm leak) 2) rough engine idle/stalling when brakes applied (also indicates a vacumm leak) or 3) No power assist (brake pedal hard to push) .
If you do discover your hydraulic problem is in your RABS valve , don't forget to bleed it ,(there is a bleeder valve on it) and the rear brakes again after you replace it .
Hope this helps
Posted on Feb 06, 2009
Well with a soft braking pedal it means its a lost of pressure problem somewhere in the braking system. If you changed the master cylinder (with a brand new one not used) and blead the brakes check the disc pads and shoes then there is a leak somewhere in the system. Start from the braking fluid work your way in the master cylinder then through the lines you will find it. One way to check if the master cylinder is loosing compression is to
1.) Take the cap of the brake fluid container
2.) start the car leave it in park or neutral
3.) have some push the braking pedal right down as they are doing this look for air bubbles in fluid container, in some cases you will need to pump the braking pedal to see any bubbles.
Another method is used by pumping the brake pedal to see if it hardens up. Usually i find this problem to be caused by rubber seals in the master cylinder. usually one or more of them is damaged. You can repair the master cylinder by using a kit for it sold at automotive stores.
If the cylinder is brand new you have a small air leak some where in the lines causing the lost of compression. It might just be small enough to leak air with small amounts of fluid that may not be noticed. (it dont have to be by the wheels it could be anywhere along the lines) you may want to consider doing a compression test at a service station to see if this is so.
Posted on Oct 31, 2008
If there is no fluid loss, most likely there is still air in the system. Did you bench bleed the master cyl before installation? How are you bleeding the system?? Manual or power bleed? Also pull a vacuum test on the booster
Posted on Oct 31, 2008
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